As NASA evolves, what will replace the shuttle?

Squinting up into the bright sky, more than 400,000 people waited for Discovery in the California desert on that October morning in 1988.
The space shuttle program had been grounded for almost three years after the Challenger disaster. But the successful flight of space shuttle Discovery felt like a new beginning to the crowd. People whooped and sobbed as the shuttle punched out two sonic booms and glided to a landing at Edwards Air Force Base.
Almost 17 years later, Discovery is again returning the grounded space program to flight